For nearly 40 years, Milt Rosenberg was the smartest man on the radio.

As host of “Extension 720,” the University of Chicago psychology professor presided over a two-hour nightly meeting of the minds on Tribune Broadcasting news/talk WGN AM 720.The program attracted a national following by virtue of WGN’s powerful signal at night and later reached a worldwide audience through multiple digital platforms.

Milton J. Rosenberg died Tuesday of pneumonia and its complications after entering the hospital on New Year’s Day, according to Joseph Morris, an attorney and close friend. He was 92.